Both Star League and Bureau of Mysteries can be bought at all good bookshops, and those that don't have it on the shelf should be able to order it in from the publisher easily enough.
I work for Readings, an excellent independent bookshop in Melbourne. Online purchases have free delivery anywhere in Australia, and if you request it in the comments field, I can sign and personalise your books.
Click here to buy from Readings
Or, if you'd prefer to have your books signed in person, you can visit me in the Carlton branch of the store. Please email me to arrange a day, I'm always happy to meet young readers!